Add confidence intervals for irm_kmi.get_forecasts_radar

[jdejaegh]

Each element returned by the the service irm_kmi.get_forecast_radar looks like this now:

{
    "datetime": "2024-05-30T18:10:00+02:00",
    "native_precipitation": 0.83,
    "might_rain": true,
    "rain_forecast_max": 1.09,
    "rain_forecast_min": 0.64
}